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United States Patent |
5,216,643
|
Berg
|
June 1, 1993
|
Rotary arm and optical head for a magneto-optic disk drive
Abstract
An optical disk drive includes a drive motor for rotating an optical disk
and a rotary arm having first and second opposite ends. The rotary arm is
mounted for rotation in a plane parallel to the disk plane by a mount. An
objective lens is mounted to the rotary arm adjacent the second end. The
objective lens is driven and positioned about a focus axis with respect to
the disk plane by a focus motor. A laser, detector and optics are mounted
to the radial arm. A tracking drive coil for producing a magnetic field is
mounted to the second end of the radial arm immediately adjacent the
objective lens. Permanent magnets on opposite sides of the tracking drive
coil produce a magnetic field which cooperates with the magnetic field of
the tracking drive coil to drive and position the objective lens about a
tracking axis with respect to the optical disk plane.
Inventors:
|
Berg; Thomas E. (Colorado Springs, CO)
|
Assignee:
|
Hewlett-Packard Company (Palo Alto, CA)
|
Appl. No.:
|
698244 |
Filed:
|
May 6, 1991 |
Current U.S. Class: |
369/13.32; 360/59; 369/44.13 |
Intern'l Class: |
G11B 013/04; G11B 007/12 |
Field of Search: |
369/13,44.13,110
360/59,114,66
365/122
|
References Cited
U.S. Patent Documents
3940148 | Feb., 1976 | Torrington et al. | 274/1.
|
3983317 | Sep., 1976 | Glorioso | 178/6.
|
4135721 | Jan., 1979 | Camerik | 274/1.
|
4326284 | Apr., 1982 | Elliott | 369/77.
|
4340955 | Jul., 1982 | Elliott | 369/213.
|
4403316 | Sep., 1983 | Van de Veerdonk | 369/44.
|
4517617 | May., 1985 | Tsuji et al. | 360/133.
|
4519055 | May., 1985 | Bilson | 369/37.
|
4545045 | Oct., 1985 | Baer et al. | 369/77.
|
4545046 | Oct., 1985 | Jansen et al. | 369/111.
|
4550394 | Oct., 1985 | Maeda et al. | 369/58.
|
4679904 | Jul., 1987 | Kurihara | 369/45.
|
4736356 | Apr., 1988 | Konshak | 369/772.
|
4752922 | Jun., 1988 | MacAnnally et al. | 369/32.
|
4761774 | Aug., 1988 | Ishibashi et al. | 369/44.
|
4813033 | Mar., 1989 | Baash et al. | 369/45.
|
4823214 | Apr., 1989 | Davis | 369/97.
|
4868802 | Sep., 1989 | Kobori | 369/45.
|
Foreign Patent Documents |
59-92406 | May., 1984 | JP | 369/13.
|
60-211438 | Oct., 1985 | JP | 360/114.
|
61-96540 | May., 1986 | JP | 360/114.
|
61-239449 | Oct., 1986 | JP | 360/114.
|
61-278059 | Dec., 1986 | JP | 360/114.
|
62-78754 | Apr., 1987 | JP | 360/114.
|
63-32755 | Feb., 1988 | JP | 360/114.
|
Primary Examiner: Nguyen; Hoa T.
Parent Case Text
This application is a continuation of application Ser. No. 07/401,095,
filed Aug. 31, 1989, now abandoned, which is a division of application
Ser. No. 07/246,776, filed Sep. 20, 1988 now U.S. Pat. No. 4,977,549.
Claims
What is claimed is:
1. An optical disk drive including:
a drive motor for rotating an optical disk in a disk plane;
a laser beam generating means for generating a laser beam to the disk;
a rotary arm;
a mount for mounting the rotary arm for rotary movement in a plane parallel
to the disk plane;
an objective lens means having an optical axis mounted to the rotary arm
for focusing said laser beam onto said optical disk; and
a tracking motor for applying tracking drive forces to the rotary arm at a
location on the arm opposite the objective lens means from the mount, to
position the objective lens means about a tracking axis with respect to
the optical disk, wherein the tracking motor includes:
a coil mounted to the rotary arm at the location on the arm opposite the
objective lens means from the mount; and
at least one magnet mounted adjacent the coil, wherein the coil is mounted
to the rotary arm immediately adjacent the objective lens means.
2. An optical disk drive including:
a drive motor for rotating an optical disk in a disk plane;
a rotary arm;
a laser mounted to the rotary arm for producing a laser beam;
optics mounted to the rotary arm for propagating the laser beam between the
laser and the objective lens means;
a detector mounted to the rotary arm for detecting portions of the laser
beam modulated by and reflected from the optical disk, and for producing
signals representative thereof;
a mount for mounting the rotary arm for rotary movement in a plane parallel
to the disk plane;
an objective lens means having an optical axis mounted to the rotary arm
for focusing said laser beam onto said optical disk;
a tracking motor for applying tracking drive forces to the rotary arm at a
location on the arm opposite the objective lens means from the mount, to
position the objective lens means about a tracking axis with respect to
the optical disk;
an objective lens mount for mounting the objective lens means to the rotary
arm for movement about a focus axis perpendicular to the disk plane,
wherein the objective lens mount includes:
a tubular lens support having a longitudinal axis, the objective lens means
fixedly mounted to the lens support and having said optical axis in
parallel alignment with the longitudinal axis, wherein the tubular lens
support includes:
a lens mount section in which the objective lens means is mounted;
a support mount section; and
a prism cage section having a laser beam receiving aperture between the
lens mount section and the support mount section, the lens mount section,
support mount section, and prism cage section being positioned with
respect to one another about the longitudinal axis;
a resilient mount coupled to said support mount section for resiliently
mounting the lens support to the rotary arm with the longitudinal axis
parallel to the focus axis, wherein the resilient mount includes:
a first leaf spring for supporting the support mount section of the lens
support with respect to the rotary arm; and
a second leaf spring for supporting the lens mount section of the lens
support with respect to the rotary arm;
a focus motor for driving and positioning the objective lens means about
the focus axis; and
a prism fixedly mounted to the rotary arm and positioned inside the prism
cage section of the lens support, for reflecting a laser beam between the
beam receiving aperture and the objective lens means.
3. An optical disk drive including:
a drive motor for rotating an optical disk in a disk plane;
a rotary arm;
a mount for mounting the rotary arm for rotary movement in a plane parallel
to the disk plane;
an objective lens means having an optical axis mounted to the rotary arm
for focusing a laser beam onto said optical disk;
a tracking motor for applying tracking drive forces to the rotary arm at a
location on the arm opposite the objective lens means from the mount, to
position the objective lens means about a tracking axis with respect to
the optical disk;
a laser mounted to the rotary arm for producing said laser beam;
optics mounted to the rotary arm for propagating the laser beam between the
laser and objective lens means; and
a detector mounted to the rotary arm for detecting portions of the laser
beam modulated by and reflected from the optical disk, and for producing
signals representative thereof.
4. A magneto-optical disk drive including:
a drive motor for rotating a magneto-optical disk in a disk plane;
laser beam generating means for generating a laser beam to the disk;
a rotary arm;
a mount for mounting the rotary arm for rotary movement in a plane parallel
to the disk plane;
an objective lens means, having an optical axis extending in the direction
perpendicular to the surface of the disk, mounted to the rotary arm for
focusing said laser beam onto magneto-optical disk;
a tracking motor for applying tracking drive forces to the rotary arm at a
location on the arm opposite the objective lens means from the mount, to
position the objective lens means about a tracking axis with respect to
the magneto-optical disk;
an annular permanent magnet concentrically positioned about said optical
axis of the objective lens means, said annular permanent magnet having
north and south magnetic poles being extended parallel to said optical
axis of the objective lens means for applying magnetic biasing fields of
opposite polarities to said disk; and
a positioning mechanism for positioning the magnet along the optical axis
with respect to the disk plane.
5. An optical disk drive including:
a drive motor for rotating an optical disk in a disk plane;
a rotary arm having first and second opposite ends;
a mount on the first end of the rotary arm for mounting the arm about an
axis for rotation in a plane parallel to the disk plane;
an objective lens mounted to the rotary arm adjacent the second end;
a laser mounted to the rotary arm for producing a laser beam;
optics mounted to the rotary arm for propagating the laser and objective
lens;
a detector mounted to the rotary arm for detecting portions of the laser
beam modulated by and reflected from the optical disk, and for producing
signals representative thereof;
a focus motor for driving and positioning the objective lens about a focus
axis with respect to the disk plane;
a tracking drive coil for producing a magnetic field mounted to the second
end of the radial arm adjacent the objective lens; and
permanent magnets mounted on opposite sides of the tracking drive coil for
producing a magnetic field which cooperates with the magnetic field of the
tracking drive coil to drive and position the objective lens about a
tracking axis with respect to the optical disk plane.
6. The optical disk drive of claim 5 and further including:
an annular permanent magnet concentrically positioned about an optical axis
of the objective lens; and
a positioning mechanism for positioning the magnet about the optical axis
with respect to the disk plane.
Description
BACKGROUND OF THE INVENTION
Reference is made to commonly assigned copending application Ser. No.
07/401,620, filed Aug. 31, 1989, entitled HALF-HEIGHT MAGNETO-OPTIC DISK
DRIVE.
1. Field of the Invention
The present invention relates generally to magneto-optic data recording
systems. In particular, the present invention is a rotary arm having a
distributed optical head mounted thereto, and a tracking actuator for use
in a magneto-optic disk drive.
2. Description of the Prior Art
Magneto-optic data recording technology combines the eraseability features
of magnetic data storage systems with the high data storage capacity of
optical systems. A 5.25 inch magneto-optic disk can hold up to 600M bytes
of information, 1000 or more times the amount of information that a
similarly sized magnetic floppy diskette can store. Magneto-optic disks
are also transportable and can be transferred between drives. Since the
reading, writing and erasing operations are performed with light beams
rather than mechanical heads, they have long life, higher reliability, and
are relatively immune to physical wear.
The principles of magneto-optic technology are well known. Information is
digitally stored at bit positions on a magneto-optic disk. Typical bit
positions have a diameter of 0.8 to 2.0 microns. The orientation of the
magnetic field at each bit position can be switched between a digital one
state in which its north pole is oriented upward, and a second digital
zero state in which the magnetic field is reversed and the north pole
oriented downward. The orientation of the magnetic field at each bit
position is selected by subjecting the bit position to the magnetic field
of the appropriate polarity, and heating the bit position of the disk. The
magnetic orientation of the bit position is frozen when the disk cools and
returns to room temperature.
The magnetic fields of all bit positions in an unwritten disk will
generally be oriented north poles down to represent a digital zero. When
writing information, the bit positions will be subjected to a write
magnetic bias field and heated by a high intensity laser beam. The
orientation of the magnetic fields at the written bit positions will then
reverse to north poles up. Bit positions are erased by subjecting them to
an erase bias field of the opposite polarity, and again heating the bit.
The magnetic field orientation at the erased bit positions will then
reverse and switch to north pole down.
Data is read from the optical disk using a low-power laser beam. Because of
the magneto-optic phenomenon known as the Kerr effect, the polarization of
a laser beam impinged upon the bit positions will be rotated as a function
of the magnetic orientation of the bit. The polarization of laser beam
portions reflected from bit positions on the optical disk is detected by
opto-electronic detector circuitry. Signals from the detector circuitry
are then processed to determine whether the bit position is representative
of a digital one or zero.
For purposes of convenience and protection, the optical disk is typically
positioned within an enclosure to form a cassette. The cassette is loaded
into an optical disk drive which is interfaced to a personnel computer or
other data processing system and includes the mechanical and electrical
subsystems required to write, read and erase data on the optical disk.
Optical disk drives typically include an optical head having an objective
lens for focusing the laser beam onto the optical disk, a drive motor for
rotating the optical disk, a focus servo system and a tracking servo
system. After the cartridge is inserted into the drive and its door
opened, the disk drive motor and optical head are moved with respect to
the optical disk to bring the drive motor and disk into engagement, and
the optical head into its operating position adjacent the disk. In one
known drive the optical head and drive motor are mounted to a frame
pivotally suspended within the drive to form an assembly. After the disk
is loaded into the drive, the assembly is driven to an operative position
at which the drive motor engages the disk and the optical head is
positioned adjacent the disk. The cartridge is loaded into and removed
from the drive when the assembly in in a load/unload position spaced from
the disk.
The tracking servo system is a closed force-position loop which includes an
actuator for driving and positioning the optical head or objective lens
about a tracking axis with respect to servo tracks on the optical disk. In
one CD planar, the optical head is positioned on an elongated arm opposite
a pivot mechanism from a counterweight. The arm and optical head are
driven about a tracking axis by a pair of electromagnetic motors, one
positioned between the pivot mechanism and each of the optical head and
counterweight. Another known magnetic disk drive includes a V-shaped arm
having two legs. The arm is movably mounted adjacent the disk by a pivot
mechanism located at the arm vertex. The magnetic head is mounted at the
free end of one arm, while the electromagnetic motor is mounted to the
free end of the other. Pivot bearing and arm dynamics, including play in
the bearing and bending of the arm, significantly affect the overall
performance of these tracking servo systems.
The focus servo system, also a closed force-position loop, includes a focus
actuator which drives and positions the objective lens about a focus axis
with respect to the optical disk. The focus servo system controls the
focus actuator in such a manner as to keep the laser beam properly focused
onto the optical disk. Linear electromagnetic motors are typically used a
actuators.
Other known optical disk drive mechanisms and associated tracking and focus
servo systems are disclosed generally in the following U.S. patents:
______________________________________
3,940,148 Torrington et al.
3,983,317 Glorioso
4,135,721 Camerik
4,326,284 Elliott
4,340,955 Elliott
4,517,617 Tsuji et al.
4,519,055 Gilson
4,545,045 Baer et al.
4,545,046 Jansen et al.
4,736,356 Konshak
4,752,922 MacAnally et al.
______________________________________
It is evident that there is a continuing need for improved disk drives.
Mechanical systems of the drive must be compact and reliable. The effects
of physical component dynamics upon tracking servo system response should
be mitigated as much as possible to increase the performance of the drive.
SUMMARY OF THE INVENTION
The present invention is an optical disk drive in which undesired effects
of arm dynamics in the force-position loop are substantially reduced. The
optical disk drive includes a drive motor for rotating an optical disk in
a disk plane, and a rotary arm. The arm is mounted for rotary movement in
a plane parallel to the disk plane by a mount. An objective lens mounted
to the rotary arm focuses a laser beam onto an optical disk. A tracking
motor applies driving forces to the radial arm at a location opposite the
objective lens from the mount to position the objective lens about a
tracking axis with respect to the optical disk.
In one embodiment the tracking motor includes a coil mounted to the radial
arm opposite the objective lens from the mount and immediately adjacent
the objective lens. At least one magnet is mounted with respect to the
drive motor adjacent the coils to form a linear motor.
Another embodiment includes a laser mounted to the rotary arm. Optics
mounted to the rotary arm propagate a laser beam between the laser and
objective lens. A detector mounted to the rotary arm detects portions of a
laser beam modulated by and reflected from the optical disk, and produces
signals representative thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional representation of an annular magnet and the
magnetic B field produced thereby.
FIG. 2 is a graph representing the magnitude of a the magnetic B field
generated along a central axis of a magnet (such as that shown in FIG. 1)
as a function of the distance from a pole surface of the magnet.
FIG. 3 is an illustration of portions of an optical disk drive which
include a bias field switching mechanism in accordance with the present
invention.
FIG. 4 is a detailed cross-sectional representation of a focus/bias field
switching assembly shown in FIG. 3.
FIG. 5 is a detailed cross-sectional diagram of the focus/bias field
switching assembly shown in FIG. 3 and taken from a side displaced from
the side shown in FIG. 4 by ninety degrees.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The principles upon which the bias field switching system of the present
invention is based can be described generally with reference to FIG. 1 in
which an annular or ring-shaped permanent magnet 10 and flux lines 12
characterizing its magnetic B field are illustrated. A magneto-optic media
such as disk 20 having bit positions 140 is also shown at two different
positions with respect to magnet 10 in FIG. 1. Permanent magnets such as
10 are characterized by a north pole surface N, a south pole surface S, a
central gap 14, an inner edge surface 16, and an outer edge surface 18. In
the embodiment shown, magnet 10 has flat pole surfaces N and S, and flat
edge surfaces 16 and 18. Magnet 10 has an inner diameter of dimension D1,
an outer diameter of dimension D2, and a thickness of dimension D3.
As is evident from FIG. 1, magnetic flux lines 12 emanating from pole
surfaces S and N near inner edge surface 16 converge upon one another
within gap 14. Magnetic flux lines emerging from pole surfaces S and N
near outer edge surface 18 converge upon one another beyond the outer edge
surface, rather than within gap 14. At some point between edge surfaces 16
and 18, flux lines 12 emanating from pole surfaces N and S switch from a
point of convergence at locations within gap 14 to locations beyond outer
edge surfaces 18.
As a result of the physical configuration of permanent magnet 10 and the
orientation of its flux lines 12, its magnetic field along a Y-axis
extending through a center of gap 14 perpendicular to pole surfaces S and
N varies in both magnitude and polarity with increasing distance from the
plane of the pole surfaces. Measured values of the magnetic B field along
the Y-axis of a Crumax 322 magnet having an inner diameter D1 of 8.27 mm,
an outer diameter D2 of 12.87 mm, and a thickness D3 of 0.30 mm, is shown
in FIG. 2. As is evident from FIG. 2, at distances between 0.0 and 1.25 mm
(i.e. y1), the magnetic field has a positive value greater than 0.3KGauss,
the threshold required to erase data on magneto-optic disk 20 (i.e., the
erase threshold). At distances between 4.0 and 5.75 mm, the field has a
value less than the -0.2KGauss write threshold required to write data to
disk 20.
The above-described characteristics of permanent magnet 10 can be
efficiently used to provide required write and erase magnetic fields for a
magneto-optic media. Referring again to FIG. 1, when the recording medium
is positioned at a distance y1 from pole surface S, bit positions 140 of
magneto-optic recording disk 20 along the Y-axis of the magnet will be
exposed to a magnetic field having a value greater than or equal to the
required erase threshold. When the recording medium is positioned at
distance y2 from pole surface S, bit positions 140 of disk 20 along the
Y-axis will be exposed to a magnetic field having a magnitude less than or
equal to the required write threshold.
Portions of a magneto-optic disk drive 50 which make use of the
above-described porperties of magnet 10 to write, read and erase data on
magneto-optic disk 20 are illustrated generally in FIG. 3. In addition to
magneto-optic disk 20, disk drive 50 includes a rotary arm 52 and tracking
drive magnet assembly 54. Disk 20 has a plurality of generally
concentrically positioned and radially spaced recording tracks 56, and is
rotated about a central axis by a drive motor (not shown).
Rotary arm 52 is formed by an actuator arm assembly 58 and a tracking drive
coil assembly 60. Tracking drive coil assembly 60 can be manufactured as
an integral unit with actuator arm assembly 58, or as a separate assembly
which is subsequently fastened to the actuator arm assembly. Rotary arm 52
is mounted about an axis 62 for rotational movement in a plane parallel to
that of disk 20. Tracking drive magnet assembly 54 is fixedly positioned
with respect to disk 20 and supports a pair of generally planar permanent
magnets 64 (only one of which is illustrated in FIG. 3) on opposite sides
of tracking drive coil assembly 60. Wire coils 66 are rigidly mounted to
coil assembly 60 at positions between magnets 64 of assembly 54. A
magnetic field generated by coils 66 in response to tracking drive signals
applied thereto will interact with the magnetic field of permanent magnets
64, and drive rotary arm 52 about a radial tracking axis 68 with respect
to disk 20. The magnitude and polarity of tracking drive signals applied
to coils 66 can be controlled in a manner which causes optical components
mounted to arm 52 and described below to track, or remain centered over, a
desired servotrack 56 on or from which information is being written, read
or erased.
All optical and opto-electronic components including laser diode 70, beam
shaping prism 72, turn-around prism 74, columnator lens 76, polarizing
beam splitter 78, detectors 80 and 82, and focus/bias field switching
assembly 84 are mounted to rotary arm 52. A radiation beam 86 is generated
by a laser diode 70, and an incident portion directed toward focus/bias
field switching assembly 84 by prism 72. Assembly 84 focuses the incident
portion of beam 86 and impinges it upon a servotrack 56 of disk 20. When
writing or erasing information on servotracks 20, laser diode 70 will
generate a beam 86 having a sufficiently high intensity to heat bit
positions 140 to the temperature needed to switch their magnetic
orientation in the presence of the write and erase bias fields.
A relatively low intensity beam is produced by laser diode 70 when
information is being read from disk 20. After being modulated as a
function of the magnetic orientation of bit positions 140 (FIGS. 1, 4 and
5), a reflected portion of beam 86 is directed through prism 74 and lens
76 before being impinged upon beam splitter 78. Beam splitter 78 divides
the beam into two separate polarization components which are impinged upon
one of detectors 80 and 82. A differential signal derived from the signals
produced by detectors 80 and 82 represents the information read from disk
20 (i.e., the digital states of bit positions 140).
Focus/bias field switching assembly 84 is mounted to a cylindrical housing
88 which is preferably fabricated as an integral section of actuator arm
assembly 58. Focus/bias field switching assembly 84 includes a focusing
subassembly 90 and a bias field subassembly 92 which are illustrated in
conjunction with a portion of optical disk 20 in FIGS. 4 and 5. Focusing
subassembly 90 includes a generally planar metallic pole piece 94,
objective lens support 96, objective lens 98 and prism 100. Pole piece 94
is a circular member bonded by epoxy to a first or lower edge of housing
88. Pole piece 94 has a circular central aperture 95 and a pair of
elongated apertures 102 positioned on opposite sides of the central
aperture. A pair of permanent magnets 104 are bonded to opposite sides of
each elongated aperture 102, and are radially spaced from one another with
respect to central aperture 95.
Lens support 96 is preferably a one-piece plastic member which includes a
lower mounting section 105, middle prism cage section 106 and upper lens
mount section 108. As shown in FIGS. 4 and 5, sections 105, 106 and 108 of
lens support 96 are vertically spaced about the path of beam 86. One side
of prism cage section 106 has a beam opening 116 which extends into prism
cavity 112. An elongated opening 114 extends through lens support 96
between lens mount section 108 and prism cavity 112, forming a path for
beam 86. Objective lens 98 is mounted within lens mount section 108 of
lens support 96. Prism 100 is positioned within cavity 112 and is fixedly
mounted to housing 88 by means of supports such as 113 (FIG. 5). Beam
opening 116 which extends into prism cage section 106 of lens support 96
is aligned with an opening 118 which extends through housing 88. Incident
portions of beam 86 directed to focus/bias field switching assembly 84
pass through openings 118 and 116 before being reflected by prism 100,
directed through lens 98, and impinged upon disk 20. Portions of beam 86
reflected from disk 20 traverse an identical path before they are directed
back to turn-around prism 74.
A pair of leaf-type springs 120 movably support lens support 96 within
housing 88, with its lower mounting section 105 extending through aperture
95 of pole piece 94. Each spring 120 has a circular outer rim 122, a
circular inner rim 124, and a leaf member 126 extending between the inner
and outer rims. Outer rim 122 of one of springs 120 is bonded to a lower
edge of pole piece 94, while its inner rim 124 is secured to mounting
section 105 of lens support 96 by fastening plug 128. The other spring 120
has its outer rim 122 bonded to an upper edge of housing 88 and its inner
rim 124 secured to lens mount section 108 of lens support 96.
A pair of wire coils 130 are secured to opposite sides of lens support 96.
As shown in FIGS. 4 and 5, coils 130 extend into elongated apertures 102
between magnets 104. Focus drive signals produced by a focus servo system
(not shown) are applied to coils 130. Magnetic fields generated by coils
130 interact with the magnetic fields between magnets 104 Lens support 96
is then driven against a bias force of springs 120 along a focus axis
generally perpendicular to disk 20. Incident portions of radiation beam 86
are thereby focused onto individual bit positions 140 by objective lens
98.
Bias field assembly 92 includes an annular permanent magnet 10 such as that
described above, and an actuator mechanism 142 for driving the magnet
between its write and erase positions with respect to disk 20. Actuator
142 includes a ring-shaped plastic coil form and magnet housing 144 which
is mounted to an upper edge of arm housing 88 by means of mounting ring
146. Housing 144 includes two sets of coils 148 and 150 wound about
recesses in its exterior surface.
Actuator assembly 142 also includes magnet sliding guide 152 which has a
ring-shaped magnet receiving face 154 and a plurality of legs 156 which
extend downward into housing 88 from magnet housing 144. As shown, ring
magnet 10 is mounted to face 154 of guide 152. Magnet 10 and face 154 of
guide 152 are concentrically positioned around lens mount section 108 of
lens support 96. Magnet 10 and guide 152 are movable within magnet housing
144 between a write position illustrated in solid lines in FIG. 5, and an
erase position illustrated in broken lines. When in its write position,
magnet 10 will be positioned at a distance such as y2 from disk 20, and
impinge a magnetic B field having a value less than or equal to the write
threshold upon bit positions 140 on which objective lens 98 is focusing
beam 86. When moved to its erase position, magnet 10 will be at a distance
such as y1 from disk 20. A magnetic B field having a value greater than or
equal to the erase threshold is then impinged upon bit positions 140,
permitting data to be erased from these bit positions.
Guide 152 prevents magnet 10 from becoming cocked and wedged within magnet
housing 144 while it is being driven between its write and erase
positions. As shown in FIG. 5, portions of legs 156 ride along an interior
surface of housing 88 while guide 152 and magnet 10 are moved together.
Magnet housing 144 also includes several grooves 158 on its interior
surface. Guide lugs 160 which extend radially outward from the edges of
guide face 154 ride within grooves 158. Lugs 160 engage mounting ring 146
when magnet 10 is in its write position, and prevent further movement of
the magnet and guide 152 from disk 20. The movement of magnet 10 in a
direction toward disk 20 is limited to the erase position when lugs 160
engage the upper ends of grooves 158. Magnet 10 is held in both the write
and erase positions by its magnetic attraction to ferro-magnetic members
162. Members 162 are mounted within recesses in the interior surface of
magnet housing 144 adjacent magnet 10 in both its write and erase
positions. The size of members 162 and the distance between them and edges
18 of magnet 10 can be adjusted to control the retaining force tending to
hold magnet 10 in its write or erase positions.
As shown in FIG. 5, coils 148 and 150 are located in planes parallel to
pole surfaces S and N of magnet 10. Coils 148 are positioned on magnet
housing 144 in such a manner that the center 166 of the plane in which
they located is positioned closer to the top edge of the magnet housing
than the center 168 of width dimension D3 of magnet 10 when the magnet is
in its erase position. Coils 15 are positioned on magnet housing 144 at
such a location that the center 170 of the plane in which they are located
is closer to the lower edge of the magnet housing than center 168 of
magnet 10 when the magnet is in its write position.
Coils 148 and 150 are connected in series with one another and function in
a solenoid-like manner. As indicated by the dot and arrow current flow
convention used in FIG. 4, coils 148 are wound in a direction opposite
that of coils 150. In response to a bias field select pulse of a first or
positive polarity applied to coils 148 and 150, the magnetic fields
generated by the coils will interact with the magnetic fields of magnet 10
and force the magnet to its write position. Magnet 10 will be held in the
write position by the force of attraction with ferro-magnetic members 162
adjacent coils 150. When a bias field select pulse of a second or negative
polarity is applied to coils 148 and 150, the magnetic fields generated by
these coils will interact with the field of magnet 10 and force the magnet
to its erase position. Magnet 10 will be held in its erase position by the
attractive force with ferro-magnetic members 162 adjacent coils 148. The
polarity of the bias field select pulse applied to coils 148 and 150
therefore determines whether magnet 10 is located in its write or erase
positions.
Bias field subassembly 92 has considerable advantages over prior art
systems used to generate write and erase bias fields. The subassembly
includes only a few parts, none of which need to be manufactured to high
tolerances. The subassembly is therefore relatively inexpensive. It is
also compact and low mass, enabling the subassembly to be carried by the
rotary arm. The bias field state is easily controlled and quickly switched
by a select pulse. Continuous current flow need not be applied to produce
either the write or erase fields. Heat dissipation can therefore be
reduced. All of these features facilitate the use of the subassembly in a
half-height drive.
Although the present invention has been described with reference to
preferred embodiments, workers skilled in the art will recognize that
changes may be made in form and detail without departing from the spirit
and scope of the invention.
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